In a wireless cellular communications system, multiuser multiple-input multiple-output (MU-MIMO) is a promising technique to significantly increase the cell capacity. In MU-MIMO, the signals intended to different users are simultaneously transmitted with orthogonal (or quasi-orthogonal) precoders. On top of that, the concept of a joint optimization of multiuser operation from both transmitter and receiver's perspective has the potential to further improve multiuser system capacity even if the transmission/precoding is non-orthogonal which could come from, for example but not limited to, the simultaneous transmission of a large number of non-orthogonal beams/layers with the possibility of more than one layer of data transmission in a beam. Such non-orthogonal transmission could allow multiple users to share the same resource elements without spatial separation, and allow improving the multiuser system capacity for networks with a small number of transmit antennas (i.e. 2 or 4, or even 1), where MU-MIMO based on spatial multiplexing is typically limited by wide beamwidth. An example of such joint Tx/Rx optimization associated with adaptive Tx power allocation and codeword level interference cancellation (CW-IC) receiver is recently a remarkable technical trend, including non-orthogonal multiple access (NOMA) and other schemes based on superposition coding.
When CW-IC is used, it is helpful if the soft buffer of the receiver is reserved for not only the desired transport block (TB) but also the interfering TBs to be handled by CW-IC. In so doing, the soft channel bits of interfering TBs at multiple (re)transmissions can be combined to enhance the success rate of data decoding. However, since the UE performing CW-IC has no idea about whether the interfering TB is a new transmission or a retransmission, the UE does not know whether soft packet combining is to be performed for the interfering TB. A solution is sought.